The present invention relates to systems and methods for manufacturing substrates. More particularly, the present invention relates to a contamination analysis unit and method for inspecting pollutants remaining on the surface of a cleaned reticle, and a reticle cleaning system.
Semiconductor devices are fabricated by way of plural processes such as ion implantation, deposition, diffusion, photolithography, etching, and so forth. Among those processing steps, photolithography is used for shaping designed patterns on a wafer. Photolithography is carried out by conducting the steps of coating a photoresist film on a wafer, exposing the wafer by transcribing the mask pattern into the photoresist film on the wafer, and then developing the pattern on the wafer by removing the photoresist film from specific regions thereon.
In the exposing step, a reticle is used as a mask that has a circuit pattern. During the exposing step, a pellicle (i.e., a thin and transparent film) is adhered to the reticle in order to protect the surface of the reticle from pollutants such as floating particles. The reticle is cleaned of pollutants at various periods of time. Often a first pellicle is removed from the reticle to clean the reticle and a new pellicle is then adhered to the reticle after cleaning the reticle.
With an increase of integration density in semiconductor devices, the reliability and yield thereof becomes lower due to pollutants on the molecular level that have not previously been considered as troublesome contamination. This is a particular concern when conducting the exposing step under the condition that various pollutants, e.g., ammoniums (NH3), sulfuric acids (SOx), or organic substances, remain on the reticle. Light irradiation of the reticle can induce optical reactions of the pollutants, and a haze on the surface of the reticle results. This degrades transmissivity of the reticle, and may result in detrimental critical dimension or pattern bridging effects on a pattern formed by the photoresist film.
To prevent these problems related to the reticle, one usually analyzes contamination on the surface of the reticle, on which light is irradiated, (hereinafter, referred to as the ‘target side’) after cleaning the reticle. Generally, a unit for cleaning the reticle and a unit for analyzing contamination of the reticle are provided at respective independent stations. After cleaning the reticle by a reticle cleaning system, an operator requests contamination analysis of the reticle from the contamination analysis station and then is informed of an analyzed result. Thus, it can take significant time for the operator to be informed of the analyzed result after cleaning the reticle, so that a number of reticles must be prepared in order to enhance the rate of operation of an exposing unit.
In the meantime, the contamination analysis to the reticle surface is generally carried out such that the target side of the reticle is placed face upward and a small amount of deionized water at room temperature is supplied to the target side. After a predetermined time when the deionized water is supplied, the deionized water on the target side of the reticle is delivered to an analysis unit such as a high-performance ion chromatography (HPIC) analyzer for examining contamination.